Supported catalysts are used on a large scale in different fields of industry. In addition to catalysts which have been applied to finely divided support materials, catalyst layers applied to sheetlike supports have also already been described.
DE 198 39 782 A1 describes metallic reaction tubes with catalytic coating. The coating is a multimetal oxide material comprising molybdenum and bismuth, which is applied directly to the reaction tube. There are no adhesion-promoting intermediate layers.
DE 199 04 692 A1 describes a structured adsorber system for removal of pollutants with low concentration from process gases, waste air or ambient air. This system comprises an adsorptive layer applied to a support and at least one catalyst layer; in this case, a temperature varying with time is imposed along the flow direction on at least one adsorption layer in the phase of desorption. What is described is a metallic support which has, on the surface, an oxidic adhesive layer to which the adsorbent or the catalyst has been applied. The material specified for an oxidic adhesive layer is aluminum oxide.
DE 603 08 698 T2 describes a microchannel reactor with bound catalyst. One of the examples discloses a silica-coated aluminum plate. This coated surface is chemically modified with a solution of N,N-dimethylpropylaminotrimethoxysilane, and used as a catalyst for the Michael addition of methyl vinyl ketone and nitroethane to give 5-nitrohexan-2-one. The use of adhesion-improving layers is not described.
DE 695 23 684 T2 describes a catalyst for cleaning of automotive exhaust gases. This catalyst consists of a support and two catalyst layers applied thereto. Intermediate layers for improving adhesion are not disclosed.
DE 10 2005 038 612 A1 discloses a process for producing membranes coated with catalyst on both sides for use in electrochemical devices. This involves producing two semifinished parts by applying an ionomer layer to a support in each case, and applying an anode catalyst layer or a cathode catalyst layer thereto. After the drying of the catalyst layers, the particular supports are removed and the two ionomer layers are bonded to one another so as to form a membrane which has an anode catalyst layer and a cathode catalyst layer.
DE 10 2005 019 000 A1 describes catalytically coated supports with porous catalyst layers, and catalyst layers comprising cavities. These are notable for high adhesive bond strengths. This document also describes the possibility of using an adhesion promoter layer between substrate and catalyst layer; the thickness thereof is typically 100 nm to 80 μm, and the layer is formed from materials which do not have any individual structures of diameter more than 5 μm. Further details of the nature of this adhesion promoter layer are not to be found in the document.
EP 0 246 413 A1 describes a plate-shaped catalyst for reducing the level of nitrogen oxides in flue gases. To improve the adhesion between support plate and catalyst material, an intermediate layer of ceramic material is provided, which has been applied by plasma spraying or by flame spraying. The sole example of a ceramic material mentioned in this document is titanium dioxide.
DE 10 2004 048 974 A1 describes an oxidation catalyst for the removal of pollutants from oxygen-rich off-gases and a process for its manufacture. The catalyst comprises tin oxide, palladium and a carrier oxide, wherein said carrier oxide is a nanoparticulate material. Thus a catalyst is disclosed comprising selected active materials which are deposited on a nanoparticulate oxide. From these catalysts deposited on a carrier mouldings can be formed, for example, or these catalysts can be used to coat a honeycomb material. The nanoparticulate oxide can be manufactured, among others, by using flame pyrolysis. A deposition of catalytically active materials on a sheet-like carrier equipped with a primer layer is not disclosed.
It is known that, for improving the adhesion of organic coatings, for example of lacquers, silicon oxide layers applied by plasma spraying, especially by flame spraying, are advantageous. Such processes are known, for example, as CCVD processes (“combustion chemical vapor deposition”). One example thereof is the Pyrosil® process, which is already being used commercially to obtain adhesion-improving surfaces.
In the field of dental prostheses, processes for producing metal-plastic bonds are known. For instance, DE patent 34 03 894 describes the production of a metal-plastic bond by the “Silicoater process”. This involves applying a thin, glasslike SiOx—C layer to a sandblasted metal surface by means of a flame hydrolysis burner, then applying an activated adhesive silane, sealing the surface thus formed with an opaque layer and then applying a plastic to this layer. DE 42 25 106 A1 discloses a further process for producing metal-plastic bonds, in which an adhesion-promoting oxide layer is formed on a metallic part and is then bonded to a plastic via an intermediate layer composed of an adhesive silane. The adhesion-promoting oxide layer is generated by decomposition of an organosilicon or organometallic compound in a spark gap.
Proceeding from this prior art, it is an object of the present invention to provide a catalyst-coated support which is notable for excellent adhesion of the catalyst layers.
The invention further provides an easily performable process for coating of sheetlike supports with catalysts, which works with readily obtainable and inexpensive materials and is therefore economically advantageous.